Abstract:

This paper deals with the appropriate traits and optimum age of early selection to improve individual volume of Chinese fir (Cunninghamia lanceolata Hook) through clonal selection. The estimated parameters of early selection were based on height and diameter at breast height (DBH) measured from two clonal trials, which included 18 and 17 clones respectively, and were as parts of a large scale clonal breeding program. At the same time, there were two kinds of CK in each trial, which came from a first generation seed orchard and a superior seed source respectively. In the spring of 1987 and 1988, one-year-old rooted cuttings and seedlings were planted with 5～6 trees in a row plot in randomized complete blocks, with 5 replications at 2 m×1.7 m spacing. Height was measured every year after planting for trial 1, and at the second year after planting for trial 2, while DBH was measured at the third year after planting for the two trials. The last investigation was taken in 1997 for trial 1 with 11-year-old and trial 2 with 10-year-old, and the individual volume of this year was calculated according to the standard volume table for Chinese fir. The genetic variances, heritabilities, genetic and phenotypic variation coefficients and juvenile mature correlations of height and DBH were estimated. Meanwhile, the genetic and phenotypic correlation between the height, DBH measured at different ages and volume calculated were also estimated to determine the best indicator for early selection. The result showed that there were significant differences (P<0.0001) among the test materials, and very strong and stable juvenile-mature genetic correlations, and also high clonal heritabilities for height and DBH at different ages, and significant correlations among height and DBH at 3～4 years after planting and volume calculated. So the clonal selection or elimination of Chinese fir clones might be carried out reliably arround 3～4 years after planting. Since heritabilities of DBH and juvenile-mature genetic correlations of DBH with individual volume were higher than that of height at the same year, the efficiency of early phenotypic selection based on DBH was greater than that of height. The paper also noted that some mistakes could be occured in early selection because of some clones with special growth type and growth pattern such as “slim clones" and "stout clones” or “upgrading performers” and “degrading performers”. So, the early selection could be carried out by the strategy of two stages selection, the first stage selection may be conducted with height at the age of 3-year-old and the final selection completed with DBH during the period of 4～6 years after planting.

Key words: Cunninghamia lanceolata Hook, Clonal test, Juvenil-mature correlation, Heritability, Early selection